During the second year, analytical studies and phantom and animal studies will be conducted to evaluate various factors in coronary artery imaging. Dual and three energy substraction systems will be compared; live scanned and area detector systems will be compared; effects of motion and intervening iodinated structures will be assessed; spatial resolutions will be determined; and stochastic signal processing methods will be tested. In vivo human studies of carotid, aorta, and femoral arteries will be performed using a line scanned system. Analytic and animal in vivo studies will be performed using a digital fluoroscopy system. Temporal substraction using digital fluoroscopy will be compared with energy substraction using the line scanned system.